private void btnzeigen_Click(object sender, System.EventArgs e)
{
  Form2 f = new Form2();
  f.TopLevel= false;
  this.Controls.Add(f);
  f.Show();
  btnzeigen.Enabled= false;
// btnzeigen.Visible= false;
 }

private void btnSchliessen_Click(object sender, System.EventArgs e)
{
  this.Close();
 //      Form1 Form1 = new Form1 ();
}

           btnzeigen.Enablede = true;